1. Field of the Invention
The present invention relates to a high-voltage electrical bushing useful with metal-enclosed, pressure-gas insulated switchgear.
2. The Prior Art
Bushings which are used for connecting gas-insulated apparatuses and plants to overhead electrical lines usually comprise an outer ceramic insulator which is in surrounding relationship to the central conductor, and the space between the conductor and the inside of the insulator is filled with a pressurized gas, for example SF.sub.6. Such bushings also include metal flanges at opposite ends of the insulator, with one of the flanges being directly connected to the current conductor in the bushing (to thus have the same electrical potential as the conductor), the second flange being in non-contacting relationship to the conductor (to thus be at a ground potential). The second flange usually supports at least one shield electrode made of an electrically-conductive material which functions to control the voltage distribution in a radial direction inside the grounded end of the insulator, as well as in the axial direction along the outer side of the insulator. The shield electrode has its top end located a short distance up within the lower end of the insulator, and it is often supplemented with one or more shield rings located on the outer side of the insulator.
In order to maintain the electric field strength at an acceptably low level, the shield electrode has to be formed with a large internal diameter and with a large edge radius at its upper end. This requires an insulator which has a large internal base diameter; however, use of large internal base diameters results in great mechanical stresses because of the pressure created by the enclosed pressurized insulating gas. In addition, a large diameter of the insulator makes it more difficult to provide a gas-tight attachment of the insulator to other structures.
In addition to the foregoing, in order that the top part of the insulator and its metal flange have acceptable dimensions, the insulator is normally made markedly conical, which, however, makes an efficient production thereof difficult.
For the foregoing reasons, bushings of conventional design are relatively expensive.
An object of the present invention is to provide a gas-insulated high-voltage bushing which has a smaller diameter and is cheaper to manufacture than comparable bushings of conventional design.